Resistance



Dec. 19,

FIG.

J. S. P. ROBERTCN RESISTANCE Filed April 4, 1931 lllllllllllll ATTORNEY Patented Dec. 19, 1933 RESISTANCE `lames S. P. Robertcn, London, England, assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application April 4, 1931, Serial No. 527,626, and in Great Britain May 23, 1930 8 Claims.

VThis invention relates to variable electrical instruments and more particularly to variable resistances, potentiometers, inductanccs, con- .densers, switches or the like of the sliding contact type.

According to the invention the rotary movement of a knobor other operating member is converted into straight line movement of a ball or other displaceable contact member through 10 the medium of a grooved roller or the like. The ball or other displaceable contact member is preferably accommodated in and caused to traverse a resistance or other'element or elements through the medium of a spiral groove. The

groove may be formed so as to cause the resistance, inductance or other electrical characteristic to vary in accordance with any required law.

Further features of the invention will be described with reference to thel accompanying drawing in which Figs. 1 and 2 illustrate a single element potentiometer or rheostat embodying the invention. Figs. 3 and 4 illustrate a four element variable resistance embodying the invention. Figs. 5 and 6 illustrate a modification in which a tapered former supports the resistance winding and the displaceable contact is driven by an elliptically grooved cylinder and made to pass from one end of a resistance winding to the other and back to starting point in one complete revolution of the cylinder.

In Fig. 1 of the accompanying drawing, plates 7 carry a resistance element 4 which may be composed of a length of enamel insulated resistance wire wound upon a fixed cylinder or rod. The rod may be one of the support rods for the end plates 7. The end plates 7 also carry a rotatable cylinder 1, in which is formed a spiral groove 8. A ball 3 is contained in the groove and is held in contact with the resistance wire by a pivotally mounted bar 5 and a spring 6 as is shown more clearly in Fig. 2.

On turning the knob 2 the cylinder 1 rotates and the ball 3 is caused to traverse the resist- 45 ance element 4. Continuous contact with the ball is maintained by means of the contact bar 5, which also, through the medium of the spring 6, forces the ball into the spiral groove and prevents back-lash developing.

It will be'obvious that the insulation must be removed from the resistance Wire along the track of the ball.

Two resistance elements might also be placed iin parallel relationship and the single ball con- 55 tact driven along between them where simultaneous variation of two resistances or potentiometers is required. In the event of two resistance elements being employed as above mentioned, the resistance in two circuits may be varied in the same sense or the resistance in one circuit may be increased while the resistance in the other is decreased according to the manner in which the variable resista-nce device is connected up.

In the form of the invention shown in Figs. 3 and 4, four resistance elements are provided shown as 41, 42, 43 and 44 and the cylinder 1 is provided with two diametrically opposed spiral grooves. Two balls 3, are provided, each of which makes contact with two of the resistance elements. In this arrangement the spring 10 is anchored at its middle part to the bar 11 and bears at its ends against the elements 43 and 44. Thus, the elements 43 and 44 are forced into contact withthe balls and the balls are also caused to make good contact with the other two elements. A variable resistance of this. type may be employed in circuits where a plurality of adjustments have to be made simultaneously.

It is also considered within this invention to replace the resistance elements by inductance elements, the inductance being varied as the displaceable contact member moves along the Wire with which the inductance is wound.

The resistance or inductance element may also be replaced by a series of contact studs or the like so that the device may be used as a switch. The series of contact studs may be arranged in a piece of insulating material the portion of the studs .with which contact is to be made being flush with the surface of the insulation. This surface is arranged adjacent a rotary spirally grooved cylinder in such a manner that a ball contained in the groove will move along the contacts as the cylinder is rotated. A plurality of insulated contact elements and one or more cooperating displaceable contacts may be provided in cases where a number of switching operations are to be performed simultaneously. A switch of this type may be employed in connection with a number of condensers for changing the capacity in a circuit.

In Figs. 5 and 6 a resistance element 4' is wound on a tapered former to obtain a logarithmic change in resistance when a displaceableA contact member is moved over the resistance Winding. An elliptical groove 8' extending helically around the cylinder is provided in the cylinder 1' so that the ball contact 3 will be driven from one end of the resistance winding 4 to the other end and back again to its starting point in one complete turning movement of the cylinder 1'.

It may be desirable in some cases to be able to change for example the resistance of a circuit according to other than a straight line law relative to the movement of a control. In such cases the spiral groove in the cylinder 1 may be designed to have a variable pitch or may be modied in any other suitable manner. The resistance or inductance elements may be wound upon formers of other than cylindrical shape. By this means for instance a small change might be obtained at a small end of the former and a relatively larger change for the same angular movement of the control at a larger end of the former. Or again, for example, a control knob may be provided and adapted to turn to 360. The spiral groove or the shape of the former may be so designed that say 60% of the total change occurs in 100 of movement of the control knob, the remaining 40% of change being spread over the remaining 260 of movement of the knob.

It will be clear that there are other details of practical embodiments of the invention which may be modified to suit particular conditions. For example, the grooved cylinder may be made of an insulating material or of metal, according to the requirements of the circuit in which the instrument is to be used. It has been found that when bakelite or ebonite is used for the construction of the cylinder, phosphor-bronzes or stainless steel balls being employed therewith as contact members, a helix angle not greater than 60 may be used, where the helix angle is measured between a tangent of the helix and a plane perpendicular to the axis of the cylinder.

It will also be clear that the wire wound resistance elements may be replaced by graphite, carbon or other :forms of resistance elements.

What is claimed is:

1. A variable electrical device comprising an electrical resistance element, a ball contact engaging said resistance element, and a grooved rotatable cylinder to drive said ball contact along said resistance element.

2. A variable electrical device comprising an electrical resistance element, a ball contact engaging said resistance element, and a helically grooved rotatable cylinder to drive said ball contact along said resistance element.

3. A'variable electrical device comprising a plurality of electrical resistance elements, a ball contact member engaging said resistance elements, and a grooved rotatable cylinder engaging said ball contact and operating to drive said ball contact along said resistance elements.

4. A variable electrical device comprising a plurality of electrical resistance elements, ball contact members engaging said resistance elements, and a grooved rotatable cylinder engaging said ball contact members to drive said ball contact members along said resistance elements.

5. A variable electrical device comprising an electrical resistance element, a grooved rotatable cylinder, a ball contact membfH engaging said resistance element and said cymder, said ball contact being movable along said resistance element by rotation of said cylinder, and means in engagement with said ball contact to press said ball contact against said cylinder and said electrical resistance element.

6. A variable electrical device comprising a plurality of electrical resistance elements, a movable ball contact member engaging said resistance elements, a grooved rotatable cylinder in engagement with said ball contact member to drive said ball contact member along said resistance elements, and spring pressed means to maintain said rotatable cylinder, said ball contact, and said resistance elements in engagement.

'7. A variable electrical device comprising a plurality of electrical resistance elements, a plurality of movable ball contact members engaging said resistance elements, a double grooved cylinder engaging said contact members to move the contact members along said resistance elements, and spring means maintaining said resistance elements, contact members and cylinder in operative engagement.

8. A variable electrical device comprising an electrical resistance element, a contact movable thereover and a grooved rotatable cylinder engaging said Contact to move said contact from one end of said resistance element to the other and back to the starting point in one complete cyclic rotation of said rotatable cylinder the groove in said cylinder being elliptical and extending in the form of a helix around the cylinder.

JAMES S. P. ROBERTON. 

